Conventional after-market valve covers or rocker arm covers (RACs) comprise a thin sheet metal or plastic cover mounted on the engine head(s). These covers have a single cavity that encloses the rocker arms, valve return springs and pushrods that together actuate the cylinder valve stems. In more recent model engines equipped with a Distributorless Ignition Systems (DIS), a plurality of ignition coils, one for each cylinder in the engine, are mounted in association with the head. For the typical V8 engine, two rocker arm covers are employed, one for each bank of 4 cylinders.
Several approaches have been tried for mounting of the coils in a manner to not interfere with the cover. In Weingaertner U.S. Pat. No. 6,494,193, for example, a stepped design for a straight-4 engine is employed wherein a large shallow-height base case covers both the rocker arms and the spark plugs. There is a smaller elevated casing atop the base that contains the coils. Leads are embedded in the plastic and oil-proof boots must be used to connect the leads to the plug. This approach suffers the serious disadvantage of having no separate oil fill, requires removal of 13 bolts to remove the base cover to access the plugs, and it houses the plugs and boots in the “wet” zone, the same space as the rocker arms, where they are continuously exposed to oil and hydrocarbon vapors.
Skinner U.S. Pat. No. 6,622,711 also uses a large cover over the plugs and a separate coil cassette (container) that fits within the large cover directly over the plugs. The coils connect to the plugs via boots as in Weingaertner. Although the engine is only shown schematically, and as a straight 4, the large cover is co-extensive with the head, so the coils are in the wet zone, albeit within a separate cassette. To access the coil cassette, 16 bolts and the large cover have to be removed.
Sato U.S. Pat. No. 5,323,745 shows a single, plastic rocker arm cover over dual camshafts and valve stems with an oil/gas separation chamber mounted on the underside of the cover. The plugs are in the wet chamber defined by the cover and a coil arrangement is not disclosed, so it appears this patent is directed to a distributor-type ignition system.
Industrie Magneti Marelli in EP Application 0-512-357-A2 (Nov. 11, 1992) provides “plug-top” ignition coils located in a 2-part housing comprising upper and lower flanged housings that are bolted together (apparently 16 bolts) at the flanges. The coils are located in the housing. Projecting from the bottom is a boot that fits over the spark plugs. The top housing includes 4 caps, each providing input lead access to the coil below. This unit is independent of a rocker arm cover and rides on the plugs themselves, rather than being separately mounted, so the unit puts weight and torsional strain on the plugs.
As can be seen from such exemplary unsatisfactory designs, there is a long felt but unmet need in the art for a cleaner, tidier rocker arm and coil assembly that prevents cross contamination, yet provides full and independent access for replacement and servicing, is robust under severe service conditions, has a useful life far longer than stamped sheet metal or plastic, and is simple and faster to install.